The objective of this research will be to isolate, characterize, and learn something of the physiological significance of a pantothenic acid and/or pantetheine binding protein that occurs in blood, plasma, or serum. This binding material, presumably a protein, is believed to be distinct from acyl binding protein or even coenzyme A where pantothenic acid, or more specifically pantothenic acid and/or pantetheine, is one moiety. The binding protein is determined by a differential microbiological assay for pantothenic acid and/or pantetheine with Lactobacillus arabinosus where the assay following heat treatment of blood represents total pantothenic acid and/or pantetheine and the assay prior to heat treatment of blood represents free pantothenic acid and/or pantetheine. The difference between the two values represents pantothenic acid and/or pantetheine held by a heat labile linkage to the binding protein. Following isolation and characterization of the protein, physiological experiments will be undertaken to learn something of the significance of the protein in the transport and metabolism of the vitamin.